The present invention relates to a process for re-producing a radiation image using a stimulable phosphor sheet. The process is favorably employable in a radiation image recording and reproducing method which-utilizes stimulated emission produced from a stimulable phosphor.
As a method replacing a conventional radiography using a combination of a radiographic film and radio-graphic intensifying screen, a radiation image recording and reproducing method utilizing a stimulable phosphor is practically employed. The method employs a stimulable phosphor sheet (i.e., radiation image storage panel) comprising a stimulable phosphor, and comprises the steps of causing the stimulable phosphor to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as xe2x80x9cstimulating raysxe2x80x9d) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The sheet thus processed is subjected to a step for erasing a radiation image remaining therein, and then stored for the next radiation image recording and reproducing procedure. Thus, the stimulable phosphor sheet can be repeatedly employed.
In general, a support and a protective film are provided on the top and bottom surfaces of the stimulable phosphor sheet, respectively. The stimulable phosphor sheet usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The phosphor sheet containing no binder can be formed by:deposition process or firing process. further, the phosphor sheet comprising agglomerated phosphor soaked with a polymer is also known.
For reproducing a radiation image stored in the stimulable phosphor sheet in the form of a latent image, two processes are known. One comprises the steps of sequentially scanning the stimulating rays in such manner that the plane of the sheet may be divided into pixels, and detecting the stimulated emission with a photodetector (such as a photomultiplier tube or a photoconductive device) having am wide light-receiving surface. In this method, the pixels are formed via time series excitation. In the other process, the stimulated emission is detected with a photodetector (such as a two-dimensional solid image pickup, device or a semiconductor line sensor) to divide the plane of the sheet into pixels, and time series signals of the radiation image information are obtained by an electric circuit. The former process has some disadvantageous features. For example, a large, complex system is needed. Further, in the former process, it takes a relatively long time to perform the process.
The radiation image recording and reproducing method is often used as X-ray radiography for medical diagnosis. In that case, it is especially desired to obtain a radiation image of high quality (particularly, high sharpness for high resolution) by applying a small dose of radiation. Therefore, the stimulable phosphor sheet is required to have a high sensitivity and to provide an image of high quality.
The sharpness of radiation image is mainly affected by diffusion or scattering of the stimulating ray in the phosphor sheet in the case that the reading process is performed by the steps of sequentially scanning the stimulating rays to divide the plane of the sheet into pixels, and detecting the stimulated emission by a photo-detector having a wide light-receiving surface. In this process, the procedure for reading the latent image comprises the steps of sequentially and sweepingly applying a beam of the stimulating rays onto the surface of the sheet to induce the stimulated emission, and successively collecting and detecting the emission. If the stimulating ray diffuses or scatters (horizontally in particular) in the sheet, it excites the stimulable phosphor not only at the target spot but also in its periphery. Consequently, the stimulated emission emitted from the target position is detected together with that from the periphery. This contamination of the emissions impairs the sharpness of the resultant image. On the other hand, in the case that the pixels are formed with a photodetector such as two-dimensional solid image pickup device or semiconductor line sensor, the sharpness of radiation image is mainly affected by diffusion or scattering of the stimulated emission.
For avoiding the diffusion or scattering of the stimulating ray, it was proposed to divide a plane of the stimulable phosphor sheet (or a phosphor layer in the radiation image storage panel) into small sections (cells) with a partition reflecting the stimulating rays.
Japanese Patent Provisional Publication No. 59-202100 discloses a radiation image storage panel having a honey-comb structure consisting of many small cells filled with stimulable phosphor. The panel comprises a substrate and a stimulable phosphor layer provided thereon, and the honey-comb structure sectioned with a partition is further provided on the phosphor layer.
Japanese Patent Provisional Publication No. 62-36599 discloses a storage panel employing a support provided with many hollows regularly arranged on one surface. The hollows are filled with stimulable phosphor, and the ratio of depth to diameter of each hollow is 3.5 or more.
Japanese Patent Provisional Publication No. 5(1993)-512636 discloses a process for preparing pixel phosphor with a mold.
Japanese Patent Provisional Publication No. 2-129600 proposes a storage panel employing a support plate having many holes vertically bored and filled with stimulable phosphor.
Further, Japanese Patent Provisional Publication No. 2-280100 discloses a stimulable phosphor sheet employing a substrate having a honey-comb micro-structure filled with stimulable phosphor.
In our copending U.S. Ser. No. 09/267,645 (filed Mar. 15, 1999, a stimulable phosphor sheet comprising stimulable phosphor-containing partitions which divide the phosphor sheet to give small sections in which a stimuable phosphor is placed is described. On the interface between the partition and the stimulable phosphor-contained section, the stimulating rays are reflected.
In our copending U.S. Ser. No. 09/397,926, a stimulable phosphor sheet comprising UV light or visible light emitting phosphor-containing partitions which divide the phosphor sheet to give small sections in which a stimulable phosphor is placed is described. On the interface between the partition and the stimulable phosphor-contained section, the stimulating rays are reflected.
An object of the present invention is to provide a process for reproducing a radiation image from a stimulable phosphor sheet in which the radiation image is stored in the form of a latent image, so that a radiation image having high sharpness can be easily obtained.
Another object of the invention is to provide a stimulable phosphor sheet appropriately employable for the radiation image reproducing process of the invention.
The present invention resides in a process for reproducing a radiation image, which comprises the steps of:
scanning stimulating rays on a stimulable phosphor sheet in which a radiation image is recorded in the form of a latent image, the phosphor sheet comprising one-dimensionally extended partitions which comprise stimulating ray-reflecting material and which divide a plane of the phosphor sheet to give plural narrow sections, and a stimulable phosphor placed separately in the narrow sections, in such manner that the stimulating rays are scanned in a direction crossing the partitions, so that the stimulable phosphor produces emission;
successively detecting photoelectrically the emission, so as to obtain a series of electric signals corresponding to the latent radiation image; and
reproducing the radiation image from the electric signals.
The invention also resides in the stimulable phosphor sheet of the above-mentioned composition which is used in the radiation image recording and reproducing method comprising the steps of recording a radiographic image on the sheet as a latent image, irradiating the latent image with stimulating rays to release stimulated emission, and electrically processing the emission to reproduce the radiation image.
The scanning is preferably done using a laser beam as the stimulating rays and in a direction at an angle of 90xc2x0xc2x145xc2x0 to the direction parallel to the partitions.
In performing the radiation image-reproducing process of the invention, the stimulating rays are preferably scanned, while the stimulable phosphor sheet is moved in a direction approximately parallel to the partitions.
The stimulable phosphor sheet of the invention comprises one-dimensionally extended partitions made of stimulating ray-reflecting material, and stimulable phosphor-charged areas sectioned with the partitions. The stimulating rays are scanned on the sheet in a direction crossing the partitions so that the pixel may be assigned. Accordingly, the radiation image reading process can be easily performed, and further the stimulating rays are kept from diffusing or scattering by the partitions. By the process of the invention, a radiation image is reproduced from the stimulable phosphor sheet with high sharpness.